Metabolic pathways to sustainability: Review of Purple Non-Sulfur Bacteria potential in agri-food waste valorization

Guillaume Bayon-Vicente Laura Toubeau Manon Gilson Guillaume Gégo Nishitha Landgey Simone Krings Baptiste Leroy ^*

• University of Mons, Mons, Belgium

Agri-food waste (AFW) represents a significant fraction of the material generated by the agri-food industry, which itself accounts for almost one-third of the annual global anthropogenic greenhouse gas (GHG) emissions. Considering the growing global population and the consequent rise in food demand, the management and valorization of this waste are essential to ensure the sustainability of the entire food chain for future generations. Recycling agri-food waste offers a promising strategy to mitigate the sector's environmental impact, particularly when the waste consists of food-grade materials that enhance its intrinsic value. Retaining such products within the agri-food chain by converting them into feed or food, a process referred to as "waste upcycling", is therefore of critical importance. Purple nonsulfur bacteria (PNSB) are emerging as promising candidates for AFW upcycling due to their remarkable metabolic versatility, which allows them to metabolize a wide range of organic substrates, including carbohydrates, volatile fatty acids (VFAs), and alcohols, into valuable microbial biomass. This biomass is notably rich in superior quality proteins, vitamins, pigments, and other high-value compounds. The phototrophic metabolism of PNSB is particularly advantageous for organic matter valorization, as the carbon conversion yield approaches unity by utilizing light as an energy source.